EE 1001Digital Topics

Introduction to Electrical Engineering

Dr. Chris CarrollMWAH 252

726-7530ccarroll

Digital Logic Circuits Foundation for digital computer design Basics are easy. . .

Discrete, two-valued variables Finite number of possible functions Complex operations built from easy

basics Combinational circuits (no memory) Sequential circuits (memory)

Combinational Circuits

AND gate

Inputs Output0 0 00 1 01 0 01 1 1

OR gate

Inputs Output0 0 00 1 11 0 11 1 1

XOR gate

Inputs Output0 0 00 1 11 0 11 1 0

NOT gate

Input Output0 11 0

Sequential Circuits Memory stores “state” of the circuit Implemented with flip-flops Clock signal switches 0101… Flip-flop captures data on clock 01

change D flip-flop is one of several kinds

available D Q clock

Counters Simplest kind of sequential circuit “Count” advances once per clock 01 Count sequence determined by circuit Sequence advances unconditionally

every time the clock goes 01 Flip-flops store the “state” of the circuit

Binary UP-counter

Now Next QLQR QLQR

0 0 0 1 0 1 1 0 1 0 1 1 1 1 0 0

D QL

clock

D QR

clock

Binary DOWN-counter

Now NextQLQR QLQR

0 0 1 1 1 1 1 0 1 0 0 1 0 1 0 0

D QL

clock

D QR

clock

Gray-Code Counter

Now Next QLQR QLQR

0 0 0 1 0 1 1 1 1 1 1 0 1 0 0 0

D QL

clock

D QR

clock

3-State, Self-Starting

Now NextQLQR QLQR

0 0 0 1 0 1 1 0 1 0 0 0

1 1 1 0

D QL

clock

D QR

clock

Computer Architecture How to build a computer Many philosophies

Complex Instruction Set Computer (CISC) Reduced Instruction Set Computer (RISC)

Always three parts of any computer Central Processing Unit (CPU) Memory (for both program and data) Input/Output (I/O)

Microprocessors CPU portion of a computer on a chip Requires external memory and I/O Examples:

4004 (first microprocessor, 4-bit) 8080 (popular 8-bit) 8086 (16-bit, early PC’s used this) Pentium (32-bit, 64-bit) Others…

Microcontrollers Entire computer on a chip

Central Processing Unit (CPU) Memory Input/Output (I/O)

Easy to embed in larger systems Modern cars include 10’s of these

Hexadecimal (base sixteen!)

Uses sixteen digits, 0-9 and a-f a=10, b=11, c=12, d=13, e=14, f=15 XY16 = X * 16 + Y Or, in binary…

00002 = 0 01002 = 410002 = 811002 = c

00012 = 1 01012 = 510012 = 911012 = d

00102 = 2 01102 = 610102 = a11102 = e

00112 = 3 01112 = 710112 = b11112 = f

Advantage of hexadecimal?

Easy conversion binary ↔ hexadecimalEach 4-bits of binary is 1 hex digit

100101102 = 9616

110100102 = d216

8a16 = 100010102

c316 = 110000112

SummaryDigital is everywhere!Even analog things can be digitizedComplexity is manageableHigh performance, low cost